1. Field of the Invention
The present invention relates to a digital image filtering device which reduces the image resolution of a digital image composed of original image data when the original image data is filtered.
2. Description of the Related Art
Conventionally, matrix operations are used in the digital image filtering. If the matrix has a comparatively large size (for example a 30×30 matrix), the filter can have a remarkable filtering effect on the image, as shown in Japanese Unexamined Patent Publication (KOKAI) NO.9-251532. However, the larger the size of the matrix, the larger the number of pixels referred to in the matrix, hence the lower the image process speed.
On the other hand, if a small matrix is used, the number of the pixels referred in the matrix is small. Therefore, in this case, the image process speed can become high, but the filter can not produce an adequate filtering effect. For example, if the image data is filtered with a low-pass filter using a small matrix, the image will not become sufficiently unsharp and blurred.